Teatro Municipal is Santiago's historic municipal theatre, a central venue for opera, ballet, concerts, and international performance. Even if you are not going to a show, the building is worth a look from the outside while walking through Santiago Centro.
The theatre sits close to several of the city's main central sights, including Plaza de Armas, Iglesia San Francisco, and the museums around the old centre. Check the programme if you want to see the interior as part of an actual performance.